After the 210-million-gallon spill from the Deepwater Horizon, the chemical agent Corexit 9500 was applied from air onto the oil slick to help it degrade and aid natural bacteria in the water remove the oil faster.

The maritime area affected appeared to be getting cleaner, but scientists and government officials didn't monitor the bacteria and chemicals, according to lead study author, Samantha Joye, a marine scientist at University of Georgia.

During the research, scientists recreated the conditions of the BP oil spill in the lab, closely monitoring the effects of Corexit 9500 on oil slicks and the microbes that feed on them.

Corexit 9500 didn't lower the presence of all microbes. The chemical agent significantly increased the presence of a family of microbes called colwellia. However, they are not as good at eating oil, Dr. Joye said.

"The fact that dispersants drove distinct microbial community shifts that impacted oil degradation efficiently came as a big surprise," Joye, said in a press release. "It is critical to quantify the factors that influence the efficiency of oil biodegradation in the environment, and that includes dispersants."

"During the spill, Marinobacter were not abundant in deep-water plume samples, possibly as a consequence of dispersant applications," said study co-author Sara Kleindienst, junior group leader at the University of Tübingen in Germany. "Whether natural hydrocarbon degraders were outcompeted by dispersant degraders or whether they were directly affected by dispersant-derived compounds needs to be resolved in future studies."

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Joye suggests that much of the oil may still be on the floor of the gulf.

In July, BP agreed to pay $18.7 billion – paid out over 18 years – to settle all government claims that have arisen from the massive spill, which killed 11 workers and destroyed businesses and marine life.

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